1. Field of the Invention
The present invention relates generally to vehicle air conditioning systems, and particularly to a refrigerating cycle apparatus in which an evaporator is used as a radiator in a hot gas cycle by directly receiving heated gas refrigerant from a compressor, and wherein refrigerant (including oil) in the condenser side is recovered for use in the hot gas cycle upon the occurrence of predetermined conditions.
2. Related Art
In a vehicle air-conditioning system, when winter heating is required, warm engine cooling water is circulated through a heat exchanger for heating, and air is heated by the warm water. However, when the temperature of the warm water is low, the temperature of the air blown into the passenger compartment is low, and it may not be possible to adequately heat the compartment.
Japanese Patent Application Laid-Open No. Hei. 5-272817 describes a refrigerating cycle apparatus having a heating function executed via a hot gas bypass. Air can be heated by introducing gas refrigerant from the compressor directly into the evaporator, bypassing the condenser, and releasing heat to the air in the evaporator during engine start-up when the water temperature is less than a predetermined value.
Also, the high-side pressure on the delivery side of the compressor is detected, and any excess or shortage of circulating refrigerant in the hot gas bypass heating mode is detected. When there is an excess of refrigerant, some refrigerant is discharged to the condenser side. When there is a shortage of refrigerant, some refrigerant is recovered from the condenser side. Specifically, the recovery of refrigerant from the condenser side is carried out by operating the compressor with the inlet side of the condenser open and the inlet side of the hot gas bypass conduit closed (normal cooling mode).
However, in the hot gas bypass heating mode, because the high-side pressure on the compressor delivery side fluctuates due to various factors such as the cycle heating load, the compressor speed and the throttle diameter of an expansion valve in the hot gas bypass conduit, accurately identifying an excess or a shortage of refrigerant based on high-side pressure alone is difficult.
In addition to this, at the start of hot gas bypass it takes a long time for the high-side pressure to stabilize. This time typically takes at least 5 minutes. During this period, there is a shortage of heating capacity due to a refrigerant shortage, as well as an insufficient amount of oil being returned to the compressor, and consequent inadequate lubrication of the compressor.
Also, when recovery of refrigerant from the condenser is carried out during winter heating, because the outside air temperature is low and consequently the cooling heat load is extremely small, the high-low pressure difference of the refrigerating cycle is also very small. Consequently, when the compressor is a variable capacity compressor with its capacity varied via the high-low pressure difference, the capacity of the compressor remains small and does not increase, therefore often making it impossible to recover the condenser refrigerant.